This invention relates to pumps and more particularly to pumps which can be used to recirculate water from a lower level to a higher level in, for instance, a pond, fountain or waterfall.
An important objective in the design of a pond pump is that it must be relatively maintenance free and reliable as it is rarely serviced or maintained after installation. One of the problems in designing such pumps is to ensure that dirt, grit or other foreign matter does not get into the areas of the pump where it can cause excessive wear leading to the pump working intermittently or even seizing completely.
A problem with known pumps is that the impeller is generally mounted directly on the output shaft of the motor. As a result of significant pressure differences across the impeller, a substantial flow of water together with grit and other foreign matter can find its way between the impeller and shaft causing damage and wear resulting in the impeller becoming a loose fit on the shaft which can cause vibration and failure. This problem has been overcome in the prior art by either making the impeller an extremely close fit on the rotor shaft to prevent the passage of foreign matter or making it a very loose fit which allows the foreign easy. The problem with the former solution is that it requires very tight manufacturing tolerances which may not be achievable at reasonable cost. As far as the latter solution is concerned, making the impeller a loose fit on the shaft means that it wears much more quickly and cannot be constructed to a high efficiency.
Another problem with pumps of the prior art is that because they use a synchronous motor to rotate the impeller, the motor can start in either direction so the pump may include a mechanism which can reverse the direction of rotation should it be the wrong way. This is generally done using detent which is deflected out of the path of rotation of the blades of the impeller when it is rotated in its correct direction of rotation but obturates the path of the blades in the opposite direction of rotation. Thus, should the motor start to rotate the impeller in the wrong direction, before it has rotated through 360xc2x0, the blade will engage with the now fixed detent which cannot move out of its way. As a result, the detent temporarily stops rotation of the impeller and the rotor shaft in a predetermined position in which the magnetic field of the motor will cause it to rotate in the opposite direction. The impeller blades can then deflect the detent out of their way on each revolution so the impeller continues to rotate in the correct direction of rotation for pumping. The problem with these prior art arrangements is that the detent is located in the pumping chamber and therefore has to engage directly with the blades of the impeller. This means that the reversing mechanism is exposed to foreign matter in the pumping chamber such as grit or shredded plant or animal matter which can cause it to seize or work intermittently. Furthermore, because the detent engages with the blades of the impeller themselves, and it must stop the impeller at a predetermined position, the impeller design is compromised which limits the design and performance of the pump.
It is an object of the present invention therefore to provide a pump in which the impeller is mounted on the rotor shaft of the electric motor in such a way that dirt, grit or foreign matter are not entrained between said shaft and impeller to cause damage and wear thereto by eliminating the flow of water between said ports.
According to the invention therefore there is provided a pond pump comprising an electric motor enclosed in a casing having a pumping chamber with an impeller mounted thereon to pump water supplied to said chamber to an outlet, and reversing means operable to allow the impeller to rotate continuously in one direction only, with abutment means on the impeller to prevent rotation thereof in the opposite direction, wherein said reversing means is mounted on the casing and located in the pumping chamber directly behind the impeller.
Preferably the impeller has a front face and a rear face and the reversing means comprises a detent or pawl which engages with said abutment means which extend from the rear face of the impeller. The abutment means can comprise a single protrusion which extends from the rear face of the impeller but preferably comprises a pair of diametrically opposed protrusions.
In the preferred embodiment, the pumping chamber has an end wall and the reversing means are located in a recess in said end wall which is juxtaposed with the rear face of the impeller.
The impeller preferably has three blades on its front face, each blade radiating outwardly from the axis of rotation of the impeller, the end of each blade at or adjacent the perimeter of the impeller being circumferentially spaced from an adjacent blade by 120xc2x0. However, any number of blades can be provided on the impeller.
In a preferred embodiment, the motor has a drive shaft one end of which is received in a first bearing mounted in the casing, the other end being received in a blind bore in the impeller which is coaxial with the axis of rotation of the shaft, the impeller having shaft mounting means extending therefrom coaxial with the axis of rotation of the shaft which are received in a second bearing in the housing.
Conveniently the shaft mounting means on the impeller comprises a first spigot which extends from the front face of the impeller coaxial with the axis of rotation thereof.
Preferably, the blind bore has an end wall with a second spigot extending therefrom coaxial with the axis of rotation of the impeller. In the preferred embodiment, the end of the drive shaft has a coaxial aperture therein which receives and mounts the second spigot of the impeller and the first spigot is received in said second bearing in the pump housing.